Recent years have seen rapid progress in the development of electric vehicles and hybrid electric vehicles (hereinbelow referred to as “electric vehicles”) in which motor drive batteries are mounted. Batteries that are mounted in electric vehicles are naturally required to be both lighter in weight and thinner in shape to improve handling characteristics and mileage. Film-covered batteries that employ a laminate material are being developed in order to make batteries lighter and thinner. The laminate material is a thin film in which a metal layer of, for example, aluminum, and a heat-fusing resin layer are laminated with an interposed adhesive layer. In addition, the laminate material is typically of a construction in which both surfaces of a thin metal layer of, for example, aluminum are covered by thin resin layers, the resulting laminate material being not only strongly resistant to acid or alkali, but also light and flexible.
A film-covered battery in which the electricity-generating components are covered by a laminate material, although light in weight, also has low rigidity and is therefore prone to the effects of vibration and shocks, and these problems must solved if the battery is to be mounted in a vehicle. A technique of clasping and securing a film-covered battery in a case is known as a means for solving these problems. However, accommodating a film-covered battery in a case raises problems regarding cooling the film-covered battery. Failure to sufficiently and uniformly suppress increase in temperature by means of forced-air cooling to obtain adequate performance of a battery will hasten the deterioration of the battery and cause degradation of the regeneration efficiency due to increase in internal resistance.
The use of a film-covered battery as the drive source of an electric vehicle necessitates the adoption of a battery cell assemblage (herein below referred to as “combined battery”) in which a plurality of film-covered batteries are stacked in multiple layers, and further, in which the stacked batteries are electrically interconnected to obtain a desired output voltage. A technique has been disclosed in the related art in which cooling air flows uniformly between each of the batteries that make up a combined battery. JP-A-H06-001150 discloses a configuration in which the size of gaps in a parallel direction between each of the batteries in a battery case increases with increasing distance from the inlet of the cooling air. This configuration equalizes the amount of cooling air that flows through gaps in areas close to the inlets and the amount of cooling air that flows through gaps in areas distant from the inlets in order to uniformly cool each battery.